Integrated linear and angular MEMS accelerometers

Abstract

An electromechanical system (MEMS) accelerometer is described. The MEMS accelerometer may be configured to sense linear acceleration along one, two or three axes, and to sense angular acceleration about one, two or three axes. As such, the MEMS accelerometer may serve as 2-axis, 3-axis, 4-axis, 5-axis or 6-axis inertial accelerometer. In some embodiments, the MEMS accelerometer may comprise a single mass connected to at least one anchor via a plurality of tethers. In other embodiments, the MEMS accelerometer may comprise a proof mass connected to at least one anchor via a plurality of tethers and one or more shuttle masses connected to the proof mass via a second plurality of tethers. Rotational and linear motion of the MEMS accelerometer may be sensed using capacitive sensors.

What is claimed is: 
     
       1. An angular and linear accelerometer comprising:
 at least one anchor connected to a substrate; 
 a proof mass coupled to the at least one anchor via a plurality of tethers, wherein a tether of the plurality of tethers is symmetric with respect to a plane that passes through a center of the proof mass and is substantially perpendicular to the substrate; 
 a first capacitor configured to generate a first sense signal in response to rotational motion of the proof mass; 
 a second capacitor configured to generate a second sense signal in response to linear motion of the proof mass; and 
 a reference capacitor formed from an electrode disposed on the substrate and a beam rigidly connected to the substrate, the reference capacitor being configured to generate a reference signal. 
 
     
     
       2. The angular and linear accelerometer of  claim 1 , wherein the first capacitor comprises a fixed electrode connected to the substrate and a free-end beam coupled to the proof mass. 
     
     
       3. The angular and linear accelerometer of  claim 2 , wherein the proof mass comprises a mass portion having an outer edge and an inner edge, and wherein the free-end beam has a fixed end proximate the inner edge and a free end proximate the center of the proof mass. 
     
     
       4. The angular and linear accelerometer of  claim 3 , wherein the fixed electrode is a first fixed electrode and the free-end beam is a first free-end beam, and wherein the second capacitor comprises a second fixed electrode connected to the substrate and a second free-end beam coupled to the proof mass. 
     
     
       5. The angular and linear accelerometer of  claim 4 , wherein the second free-end beam has a fixed end and a free end, the fixed end of the second free-end beam being closer than the free end of the second free-end beam relative to the center of the proof mass. 
     
     
       6. The angular and linear accelerometer of  claim 1 , wherein the second capacitor is configured to generate a sense signal in response to out-of-plane motion of the proof mass, and
 wherein the second capacitor is formed from a second electrode disposed on the substrate and a portion of the proof mass. 
 
     
     
       7. The angular and linear accelerometer of  claim 6 , further comprising circuitry configured to determine out-of-plane acceleration of the angular and linear accelerometer based on the sense signal and the reference signal. 
     
     
       8. The angular and linear accelerometer of  claim 1 , wherein the electrode is a first electrode, and wherein the first capacitor is configured to sense out-of-plane motion of the proof mass in response to an angular acceleration, and wherein the first capacitor is formed from a second electrode disposed on the substrate and a portion of the proof mass. 
     
     
       9. A method for sensing angular and linear acceleration, the method comprising:
 sensing rotational motion of a proof mass connected to a substrate via at least one anchor by generating, through a first sense capacitor, a first sense signal in response to angular acceleration about a first rotational axis, wherein the proof mass is connected to the at least one anchor by at least one tether that is symmetric with respect to a plane that passes through a center of the proof mass and is substantially perpendicular to the substrate, and 
 sensing linear motion of the proof mass, wherein sensing linear motion of the proof mass comprises:
 generating, through a second sense capacitor, a second sense signal in response to linear acceleration along a first axis; 
 generating a reference signal through a reference capacitor formed from an electrode disposed on the substrate and a beam rigidly connected to the substrate; and 
 combining the second sense signal with the reference signal. 
 
 
     
     
       10. The method of  claim 9 , wherein the first rotational axis and the first axis are parallel to one another. 
     
     
       11. The method of  claim 9 , wherein the first rotational axis and the first axis are perpendicular to one another. 
     
     
       12. The method of  claim 9 , further comprising sensing linear motion of the proof mass by generating, through a third sense capacitor, a third sense signal in response to linear acceleration along a second axis different than the first axis. 
     
     
       13. The method of  claim 9 , further comprising sensing angular motion of the proof mass by generating, through a third sense capacitor, a third sense signal in response to angular acceleration about a second rotational axis different than the first rotational axis. 
     
     
       14. The method of  claim 13 , further comprising sensing angular motion of the proof mass by generating, through a fourth sense capacitor, a fourth sense signal in response to angular acceleration about a third rotational axis different than the first and second rotational axes. 
     
     
       15. An angular and linear accelerometer comprising:
 at least one anchor connected to a substrate; 
 a proof mass coupled to the at least one anchor via a first plurality of tethers; 
 a shuttle mass coupled to the proof mass via a second plurality of tethers; 
 a first sense capacitor formed at least partially from the proof mass, the first sense capacitor being configured to generate a first sense signal in response to angular motion of the proof mass; and 
 a second sense capacitor formed at least partially from the shuttle mass, the second sense capacitor being configured to generate a second sense signal in response to motion of the shuttle mass. 
 
     
     
       16. The angular and linear accelerometer of  claim 15 , wherein the second sense capacitor is configured to generate the second sense signal in response to angular motion of the shuttle mass,
 wherein the second plurality of tethers define a rotation axis for the shuttle mass, and 
 wherein the shuttle mass has a center of gravity that is offset relative to the rotation axis. 
 
     
     
       17. The angular and linear accelerometer of  claim 16 , wherein the shuttle mass comprises first and second mass portions disposed on opposite ends of the shuttle mass relative to the rotation axis, the first and second mass portions having different weights,
 wherein the second sense capacitor is formed from the first mass portion and a first electrode disposed on the substrate, and 
 further comprising a third sense capacitor formed from the second mass portion and a second electrode disposed on the substrate. 
 
     
     
       18. The angular and linear accelerometer of  claim 15 , wherein the second sense capacitor is configured to generate the second sense signal in response to linear motion of the shuttle mass, and wherein
 the second sense capacitor is formed from a free-end beam connected to the shuttle mass and a fixed electrode anchored to the substrate. 
 
     
     
       19. The angular and linear accelerometer of  claim 15 , wherein first sense capacitor is formed from a free-end beam connected to the proof mass and a fixed electrode anchored to the substrate. 
     
     
       20. The angular and linear accelerometer of  claim 15 , wherein the proof mass is heavier than the shuttle mass.